It is often desirable and sometimes even necessary that various biologically active substances be given to ruminants in order to supplement their diet. Generally, these biologically active substances are mixed with their feed in order to provide the biologically active substances to the ruminant on a daily basis. Unfortunately, it is inconvenient to supplement the feed of various ruminants since they graze for long periods of time. Therefore, it is desirable to provide such ruminants with a daily supplement which can be released in the gastro-intestinal tract over a prolonged period of time.
A variety of sustained release pellets or boluses have been disclosed in the art which provide for the release of a beneficial agent such as a nutrient or medicament. For example, U.S. Pat. No. 3,507,952 discloses a sustained release bolus for animal husbandry. These sustained dosage boluses remain in the rumeno-reticular sac of an animal over an extended period of time wherein the therapeutically active substance has a predicable and controlled release pattern. These compositions generally comprise a dense filler, a therapeutically active substance and a lubricant.
U.S. Pat. No. 3,577,513 relates to a pellet for ruminants containing magnesium or magnesium alloy and iron particles. This patent teaches that in order for the pellets, once introduced into the rumeno-reticular sac, to remain there for a considerable period of time it is necessary that the pellet be of specific gravity not less than 2.2.
While the above delayed-release or extended release tablets or capsules have been described as being suitable, most of these suffer from difficulty in manufacture and limitations on the amount of nutrients since tablets may require high levels of carriers. Therefore, there exist a need for a bolus which can be easily manufactured and is used for supplying the animals with a biologically active substance over prolonged periods of time and whereby the ratio of the components, directly control the release time of the biologically active substance.